Particulates of an inorganic oxide such as silica or alumina must generally have their surface rendered hydrophobic for obtaining an organic solvent dispersion thereof. Thus, generally, the surface of such particulates is modified.
A method of modifying the surface of such inorganic compound particulates comprises reacting, for example, a reactive monomer or a coupling agent with hydroxyl groups of the particulate surface. This method is carried out, for example, by dispersing powdery particulates in an organic solvent and adding a modifier to the dispersion to thereby modify the particulate surface, or by conducting a solvent substitution so as to replace water of an aqueous dispersion of particulates by an organic solvent and adding a modifier to the dispersion to thereby modify the particulate surface.
However, these methods cannot completely inhibit the aggregation of particulates, thereby rendering it difficult to obtain an organic solvent sol of high dispersibility.
Moreover, the problem has been encountered such that, when the above inorganic compound particulates are used as a filler in, for example, a coating material, a hard coating agent component of an insulating coat and a protective coat, adding a sol thereof to a matrix of coating film forming agent is likely to invite an aggregation of particulates in the matrix. Especially, the defect has been encountered such that, when the organic solvent sol is used in the presence of cation, anion, or surfactant, particulates may be aggregated and a gelation may occur.
For example, for the use for the coating material, in order to improve the hardness, water resistance and stain resistance of the coating films, an organic solvent sol in which the inorganic compound particulates had been dispersed has been used. However, a problem has been encountered such that the coating material becomes viscous and whitens since such organic solvent sol is poor in its compatibility with the coating film-formed resin and the resin emulsion being obtained.
Further, for the hard coating agent, in order to improve properties of the film being formed, such as the hardness and water resistance, inorganic compound particulates have been used as fillers. However, a problem has been encountered such that the hard coating film being formed therefor becomes opaque since the particulates are poor in the dispersing stability in the coating solution used in the coating film forming process. Also in the case that such organic solvent sol is used as a solution for an insulating film and a protective film forming for electrical and electronic components, and the like, the problem has been encountered such that the coating solution becomes viscous since the particulates are poor in dispersibility in the coating solution.
Furthermore, in order to improve soil strength, a sol in which inorganic compound particulates had been dispersed has been added to a cement as a soil stabilizer. In the event that the sol is poor in stability, the problem has been encountered that it has been hard to fill up crevices between the soils and moles with the inorganic compound particulates.